1. Field of the Invention
The present invention relates in general to selectively providing power to at least one component of a vehicle-based control module for determining the presence and validity of a RF signal transmitted by a remote device.
2. Description of the Related Art
Remote vehicle entry transmitters are used for performing a wireless operation on a vehicle such as locking and unlocking a door, unlatching a trunk latch, or activating or deactivating an alarm system equipped on the vehicle. These remote entry devices are commonly referred to a remote keyless entry (RKE) fob. The RKE fob is typically a small rectangular or oval plastic housing with a plurality of depressible buttons for activating each one of the wireless operations. The RKE fob is carried with the operator of a vehicle and can wirelessly perform these functions when within a predetermined reception range of the vehicle.
The RKE fob transmits a RF signal to a keyless entry module located within the vehicle. The keyless entry module receives the transmitted RF signal and determines the validity of the signal. If the RF signal is validated, then one of the vehicle entry functions is activated. In determining whether the RF signal is valid, bits of data transmitted in the RF signal are transmitted to a microcontroller via a communication line for processing and determining the validity of the RF signal. During an engine-on condition, power supplied to the keyless entry module is supplied by a vehicle alternator so power utilized by the keyless entry module to monitor for a RF signal is not an issue with power consumption. However, during engine off conditions, the battery is used to power the keyless entry module which if constantly on, would cause a drain on the battery.
Typically, to reduce the current consumption of the receiver and the microcontroller (i.e., of the RKE) while awaiting receipt of a transmitted signal for processing, the receiver and microcontroller enter a sleep state. The receiver and the microcontroller are woken from the sleep state on a periodic basis to check for and the validity of a received RF signal. Typically the receiver is on for a duration of time 4 msec to receive a RF signal and to transmit the RF signal to the microcontroller while allowing the bits to stabilize so that a determination can be made that the RF transmission is valid. The receiver and controller then re-enter the sleep state until a next timed wake-up is required for monitoring for a next incoming RF signal. A strobing circuit supplies the power to the receiver and the microcontroller for energizing the receiver and microcontroller from the sleep state so that an RF signal may be received, processed, and validated.
In a remote keyless entry system, for the majority of the time that a receiver is in an energized state no transmitted RF signal will be received. This is due to the infrequent activation of a vehicle entry transmitter. However, the receiving circuit must be continuously energized for those few occurrences when a RF signal is transmitted. As stated earlier, the strobing circuit periodically energizes the receiving circuit for energy conservation as opposed to providing a constant flow of current to the receiving circuit. The strobing circuit will provide the same amount of current during each wakeup state regardless if a transmitted RF signal is present or not present. This is required so that when a RF signal is transmitted and received the proper amount of time is allocated for processing the RF signal and for making the determination of the RF signal's validity. Periodically energizing the receiver for a respective duration that is sufficient to process a RF signal results in unnecessary power consumption during those periods when a signal is not received.